The present study, "Substituting Environmentally Relevant Flame Retardants: Assessment Fundamentals", was commissioned by the German Federal Environmental Agency (Umweltbundesamt, ⁠UBA⁠) and prepared during the period from September 1998 to December 2000. The present status, as well as trends and alternatives, with regard to the application of flame retardants in selected products of the construction sector, the electrotechnical and electronics industry, the rail vehicle sector, and the textile industry, are examined. In parallel, 13 flame retardants which are important in terms of their substance streams and toxicology/ecotoxicology are characterized and evaluated in detail with regard to their substance properties.